What are the causes of the mold burst?

1. The mold material is not easy to be broken in subsequent processing.

Die life of different materials is often different. To this end, two basic requirements are imposed on the material of the die working parts:

1 The material should have high hardness (58~64HRC) and high strength, high wear resistance and sufficient toughness, small heat treatment deformation and certain thermal hardness;

2 process performance is good. The processing and manufacturing process of die working parts is generally more complicated. Therefore, it is necessary to have adaptability to various processing processes such as forgeability, machinability, hardenability, hardenability, quench crack sensitivity, and grinding processability. Generally, according to the material characteristics, production batch, precision requirements, etc. of the stamping parts, the high-performance mold materials are selected, and the craftability and economy are taken into consideration.

2. Heat treatment

Improper quenching and tempering process

Practice has proved that the hot processing quality of the mold has a great influence on the performance and service life of the mold. From the analysis and statistics of the causes of mold failure, it is known that the mold failure 'accident' caused by improper heat treatment accounted for more than 40%. The quenching deformation and cracking of the working parts of the mold, and the early fracture of the working process are all related to the hot working process of the tool.

Forging process: This is an important part of the manufacturing process of mold parts. For molds of high alloy tool steels, technical requirements are often imposed on metallographic structures such as material carbide distribution. In addition, the forging temperature range should be strictly controlled, the correct heating specification should be established, the correct forging force method should be used, and the post-forging slow cooling or timely annealing should be carried out.

Pre-heat treatment: Pre-heat treatment processes such as annealing, normalizing or quenching and tempering should be used depending on the materials and requirements of the working parts of the mold to improve the structure, eliminate the structural defects of the forged blank, and improve the processing technology. The high-carbon alloy mold steel can eliminate the reticulated secondary cementite or chain carbide after proper preliminary heat treatment, so that the carbide is spheroidized and refined, and the uniformity of carbide distribution is promoted. This is beneficial to ensure the quality of quenching and tempering and improve the life of the mold.

Quenching and tempering: This is the key link in the heat treatment of the mold. If the superheat occurs during quenching and heating, not only will the workpiece cause greater brittleness, but also cause deformation and cracking during cooling, which seriously affects the life of the mold. Special care should be taken to prevent oxidation and decarburization during die quenching. The heat treatment process specification should be strictly controlled. Vacuum vacuum heat treatment can be used if conditions permit. After quenching, it should be tempered in time, and different tempering processes should be adopted according to technical requirements.

Stress relief annealing: The working parts of the mold should be subjected to stress relief annealing after roughing. The purpose is to eliminate the internal stress caused by roughing, so as to avoid excessive deformation and cracking caused by quenching. For molds with high precision requirements, it needs to be subjected to stress relief and tempering after grinding or electric machining, which is beneficial to stabilize mold precision and improve service life.

3. The mold is not flat enough to produce flexural deformation.

The surface quality of the mold working parts has a very close relationship with the wear resistance, fracture resistance and anti-adhesion ability of the mold, which directly affects the service life of the mold. In particular, the surface roughness value has a great influence on the life of the mold. If the surface roughness value is too large, stress concentration will occur during operation, and cracks will easily occur between peaks and valleys, which will affect the durability of the die and affect the durability. The corrosion resistance of the surface of the workpiece directly affects the service life and accuracy of the die. To this end, the following matters should be noted:

a. The working parts of the mold must be prevented from grinding the surface of the burned parts. The grinding process conditions and process methods (such as grinding wheel hardness, particle size, coolant, feed rate, etc.) should be strictly controlled;

b. During the processing, the surface of the working part of the mold should be protected from macroscopic defects such as knife marks, interlayers, cracks and impact marks. The presence of these defects can cause stress concentration and become the source of the fracture, causing early failure of the mold;

c. Finishing and fine machining such as grinding, grinding and polishing to obtain smaller surface roughness values ​​and improve tool life.

4. Design process

The mold strength is not enough, the knife edge spacing is too close, the mold structure is unreasonable, the number of template blocks is not enough, there is no padding foot, the mold guiding is not accurate, and the gap is unreasonable.

1) Layout and edging. Unreasonable reciprocating feed patterning and too small edge values ​​often cause sharp wear of the mold or bruises on the convex and concave molds. Therefore, in consideration of improving the utilization rate of material judgment, it is necessary to reasonably select the layout method and the edge value according to the processing batch size, quality requirements and mold matching gap of the parts to improve the life of the mold.

2) Precision of the guiding mechanism of the mold. Accurate and reliable guiding, to reduce the wear of the working parts of the mold, to avoid the impact of convex and concave molds, especially the gapless and small gap blanking die, composite die and multi-station progressive die are more effective. In order to improve the life of the mold, it is necessary to correctly select the guiding form and determine the accuracy of the guiding mechanism according to the requirements of the nature of the process and the accuracy of the parts. In general, the accuracy of the guiding mechanism should be higher than that of the convex and concave molds.

3) Geometric parameters of the die (convex, concave die). The shape of the convex and concave molds, the fit clearance and the fillet radius not only have a great influence on the forming of the stamping part, but also have a great influence on the wear and life of the mold. For example, the matching clearance of the mold directly affects the quality of the blank and the life of the mold. For higher precision requirements, a smaller gap value should be selected; otherwise, the gap can be appropriately increased to improve the life of the mold.

5. Wire cutting process

The artificial wire cutting is performed, the wire cutting gap is not handled correctly, and the effect of the clearing layer and the line cutting is not affected.

The die edge is mostly processed by wire cutting. Due to the thermal effect and electrolysis of the wire cutting process, a certain thickness of the metamorphic layer is produced on the surface of the die, resulting in a decrease in surface hardness and microcracking, which causes the die of the wire cutting process to be prone to early wear and directly affect the punching clearance of the die. Keep and the edge is easy to chip and shorten the life of the mold. Therefore, a reasonable electrical standard should be selected in the online cutting process to minimize the depth of the metamorphic layer.

6. Selection of punching equipment

Punch tonnage, insufficient punching force, too deep adjustment.

The accuracy of stamping equipment (such as presses) and the impact of rigid on die life are extremely important. The precision of the stamping equipment is high, the rigidity is good, and the die life is greatly improved. For example, the complex silicon steel sheet die material is Crl2MoV, which is used on ordinary open presses, and the average regrind life is 1-3 million times. On the new precision press, the re-grinding life of the die can reach 6~120,000 times. Especially for small gap or gapless die, carbide die and precision die, it is necessary to select a press with high precision and good rigidity. Otherwise, the die life will be reduced, and the chess piece will be damaged in severe cases.

7. Stamping process

The thickness tolerance of the raw materials of the stamped parts is excessive, the material performance is fluctuating, the surface quality is poor (such as rust) or the unclean (such as oil stain), etc., which will cause the wear of the working parts of the mold to be intensified and easy to collapse. To this end, you should pay attention to:

1) Use as much as possible of the stamping process of raw materials to reduce the stamping deformation force;

2) Before stamping, the grade, thickness and surface quality of the raw materials should be strictly checked, and the raw materials should be wiped clean. If necessary, the surface oxides and rust should be removed;

3) According to the stamping process and the type of raw materials, softening treatment and surface treatment may be arranged as necessary, and a suitable lubricant and lubrication process may be selected.

8. Proper use and reasonable maintenance of production operations.